Mr Mursi and Mr Shafiq represent very different strands of Egyptian society.

Mr Mursi is seen as belonging to a popular strand of political Islam that was excluded from the political process for many years under Hosni Mubarak.

Mr Shafiq, who served briefly as Mr Mubarak's prime minister, is regarded by many as a creature of the old secular regime.

Analysts say he drew his support from people fearful of an Islamist takeover, and those exhausted by the upheavals of the past 16 months.

The BBC's Jon Leyne in Cairo says the two old power centres in Egyptian politics - the army and the Brotherhood - will go head-to-head in what could be a very polarised battle.

For many Egyptians it is not an ideal choice, but it seems the two candidates closest to the revolutionaries of Tahrir Square - Mr Sabbahi and former Arab League chief Amr Moussa - split that vote, our correspondent adds.

Mr Moussa appears to have come fifth - behind independent Islamist Abdul Moneim Aboul Fotouh, who is in fourth place according to most counts.

Landmark poll

It was the country's first freely contested presidential election in its history, and observers said it had been conducted peacefully.

US Secretary of State Hillary Clinton congratulated Egypt on its "historic" election and said Washington looked "forward to working with Egypt's democratically elected government," according to a statement released by her spokeswoman.

Turnout appeared to vary across the country on Thursday, the second day of voting.

In Cairo, there were long queues at some polling stations but elsewhere, such as Alexandria and Suez, there were reports of slow voting.